Snap vertices to a grid when moving
In the 3D view header, at the bottom of the 3D window change the snapping type pulldown menu to Increment, after that a button will appear by it's side allowing you to change the increment type to Absolute Grid alignment.



I am not sure but I think you can control the size of the grid in the 3D View Properties Shelf > (N menu) under the Display Panel > Grid Floor > Scale